Biogenic synthesis of novel platinum-palladium bimetallic nanoparticles from aqueous Annona muricata leaf extract for catalytic activity

This work reports the fast and effective bio-fabrication of novel platinum-palladium bimetallic nanoparticles (Pt-Pd BNPs) along with their counterparts Pt and Pd monometallic NPs (MNPs) through aqueous Annona muricata leaf extract. The bio-fabrication of the NPs was achieved within 2 h at 100 degrees C and pH 7 which was established by the occurrence of dark brown color for Pt MNPs and black color for Pd MNPs and Pt-Pd BNPs. NPs were evaluated for their catalytic activity in the reduction of methyl orange (MO), rhodamine-B (rh-B), and methylene blue (MB) textile dyes in presence of sodium borohydride as a reducing agent. Pt-Pd (1:3) BNPs showed higher MO dye degradation (96.84 +/- 2.05% in 50 min) followed by Pd MNPs (97.07 +/- 1.46% in 60 min), Pt-Pd (3:1) BNPs (97.34 +/- 1.17% in 70 min) and Pt-Pd (1:1) BNPs (98.12 +/- 1.04% in 80 min). Pd MNPs showed significant catalytic activity in the reduction of rh-B dye by 97.27 +/- 1.14% in 12 min followed by Pt-Pd (3:1) BNPs (96.76 +/- 2.17% in 18 min), Pt-Pd (1:3) BNPs (96.53 +/- 1.97% in 33 min) and Pt-Pd (1:1) BNPs (97.11 +/- 2.09% in 39 min). Pt-Pd (1:3) BNPs also showed higher MB dye degradation (96.95 +/- 1.57% in 40 min) followed by Pd MNPs (96.22 +/- 2.36% in 55 min), Pt-Pd (3:1) BNPs (97.29 +/- 1.22% in 75 min) and Pt-Pd (1:1) BNPs (96.45 +/- 2.19% in 105 min). However, Pt MNPs showed no catalytic activity. Standard disc diffusion method was used to evaluate the NPs toxicity towards Escherichia coli and Staphylococcus aureus, which showed no inhibitory zones. NPs showed less toxicity compared to potassium dichromate (control) against Artemia nauplii. Among the NPs studied, Pt-Pd (1:1) BNPs showed less toxicity with 100% mortality only at 100 mu g/mL concentration followed by Pt MNPs (>= 80 mu g/mL), Pt-Pd (1:3) BNPs (>= 60 mu g/mL), Pt-Pd (3:1) BNPs (>= 60 mu g/mL) and Pd MNPs (>= 40 mu g/mL) after 72 h exposure. These evaluations support the application of bio-fabricated Pt-Pd BNPs as nano-catalysts in textile dyes degradation.